The formula behind the result
Use total length and gate width in feet, and board width and gap in inches. Let L be total length, G the gate count, Wg gate width, Wp picket width and S the gap.
net run = max(0, L − G × Wg)
pickets = ceil(net run × 12 ÷ max(0.01, Wp + S))
The factor 12 converts feet to inches. ceil means round upward, including when only a fraction remains. The 0.01 in denominator floor is a software guard against division by zero; it is not a usable board size. Enter a real positive board width, not zero.
Same run, different gap or gate
These are hypothetical input cases tested against this site's calculation code. They are not recommended board dimensions, purchase quantities, product specifications or measurements of a real property. Every case uses a total length of 100 ft and a board width of 5.5 in.
| Gap | Gate openings | Calculation | Result |
|---|---|---|---|
| 0 in | None | ceil(100 × 12 ÷ 5.5) | 219 pickets |
| 0.5 in | None | ceil(100 × 12 ÷ 6) | 200 pickets |
| 0 in | One 4 ft opening | ceil(96 × 12 ÷ 5.5) | 210 pickets |
| 0.5 in | One 4 ft opening | ceil(96 × 12 ÷ 6) | 192 pickets |
A gap increases the width-plus-gap divisor. A gate reduces the run being divided. These changes explain the different results without assuming a material price or selecting a product for you.
Why a tiny length change can add a picket
Whole-item rounding creates steps. With hypothetical 6 in boards, no gap and no gate, a 1 ft run returns ceil(12 ÷ 6) = 2. Change the run to 1.01 ft and the calculation becomes ceil(12.12 ÷ 6) = 3. Both cases were tested with the calculator's actual code. A small increase crossing a whole-item boundary can therefore change the output; it is not evidence of a price change.
What this count does not include
The formula repeats a board-width-plus-gap interval over the net run. It does not place every board, adjust individual end gaps, calculate overlap or count a second layer. It does not add spare boards, a waste percentage, or boards for the gate leaf itself. Those are separate decisions that this output cannot settle.
This is why a material count should not be treated as an exact panel layout or a purchase-ready cut list. Compare the result with your actual fence system and planned layout before ordering. Board-on-board, double-sided or other overlapping designs are not represented by this single-layer formula.
Does post spacing change this picket count?
Not directly in this calculator. The picket branch reads the net run, board width and gap, but not post spacing. Changing post spacing can change other quantities without changing pickets. Gate openings can change pickets because they change the net run.
What if I choose chain link?
The chain-link branch does not report a picket quantity. Its result is net fabric length. Read the chain-link fabric explanation rather than applying this wood-board formula.
Method and source
This article documents this site's browser-side calculation code, specifically its net-run and vertical-infill branches. The worked cases are original software checks of that implementation. They are not construction standards, engineering advice or a claim that every fence calculator uses this method.